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What do the terms postponement, slip and scrub mean in the context of the space shuttle program?

For example, the 1986 Rogers Commission report under the 'Launch Delays' section mentions that "the launch of mission 51-L was postponed three times and scrubbed once from the planned date of January 22, 1986" and in the next paragraph says that on "January 22, 1986, the Program Requirements Change Board first slipped the launch from January 23 to January 25."

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The criteria are defined in the Space Shuttle Missions Summary page 1-3.

  • Postponements were launch delays which occurred prior to call-to-stations for OMI S0007 Shuttle Countdown.

  • Scrubs were launch date changes after the start of Shuttle countdown (countdown was terminated or recycled to a later launch date).

  • Launch Delays were delays which occur only on the day-of-launch.

"Slip" is an informal term.

Shuttle Countdown formally started at T-43 hours with 28 hours of built in hold time which adds up to 71 clock hours. (My recollection is that call to stations was 72 hours before launch, so maybe there was a hour of coffee / getting-logged-in time allowed there)

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  • $\begingroup$ Thank you. Would you say slip can be informally taken to mean any kind of delay of the launch? Or it's more specific than that? $\endgroup$ Commented 2 days ago
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    $\begingroup$ @JayBee just from reading the media back then I'd say "slip" was most often used to mean a postponement, i.e. a schedule change. Scrubs were usually called scrubs and launch delays were not that big of a deal. $\endgroup$ Commented 2 days ago
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    $\begingroup$ @JayBee I'd agree with Marble -- "schedule slip" is a common term in business settings for when a date gets pushed back a little. It's a synonym for postponement, but with the implication that it's only a minor postponement. At my company, a schedule slip is usually from a few days to a couple weeks, while a postponement likely means we're rolling out many months behind schedule and will probably require reworking the whole schedule to accommodate whatever has happened. $\endgroup$ Commented 2 days ago
  • $\begingroup$ My recollection from the early days is that a "scrub" results from a delay that's long enough that the fuel has been sitting in the tanks too long, so the tanks have to be drained, scrubbed, and refilled. $\endgroup$ Commented yesterday

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